docs: def find_file_in_zip(zip_file):
      '''Returns the twb/tds file from a Tableau packaged file format. Packaged
      files can contain cache entries which are also valid XML, so only look for
      files with a .tds or .twb extension.
      '''
  
      candidate_files = filter(lambda x: x.split('.')[-1] in ('twb', 'tds'),
                               zip_file.namelist())
  
      for filename in candidate_files:
          with zip_file.open(filename) as xml_candidate:
              try:
                  ET.parse(xml_candidate)
                  return filename
              except ET.ParseError:
                  # That's not an XML file by gosh
                  pass